Why does accelerating slowly save gas?

Question

Seems like whether you get up to speed quickly or slowly it should take the same amount of fuel.

Answer 1

I know exactly what you mean. If the engine's efficiency were independent of power output and RPM, then it wouldn't matter how fast you accelerate; getting up to a given speed (kinetic energy) would require the same amount of fuel (chemical energy) regardless. This is, however, not the case. Auto engines are optimized to perform with maximum efficiency at a cruising speed of 45-55 mph or so in top gear. The higher power needed for high acceleration, though, means a lower gear and higher RPM are required.

Answer 2

In a modern fuel-injected internal combustion engine, it doesn't make a lot of difference. For a specific vehicle, you would use the least gas by operating the engine at its most efficient RPM and power output.

In earlier days when gas was cheap and performance was king, quickly flooring the accelerator squirted raw gasoline into the barrel of the carburetor to try to coax out a little extra power for that instant.

Answer 3

Efficiency goes down when slamming on the gas pedal. This results because a large spurt of petrol (aka gasoline) is injected into the cylinders while they are moving relatively slowly. The petrol fires and pushes on the cylinders, but, because of inertia, they don't immediately come up to speed. So a lot of that energy in the big spurt of gasoline is wasted, it is not turned into motivating the car.

On the other hand, when pushing slowly on the gas pedal, smaller spurts of petrol are injected. As the cylinders begin to rev up, the slower adding of gas by a slower application of the pedal better matches the speed of the cylinders that are also slowly coming up to speed. Thus, there is less fuel going to waste; more of it is burning to propel the car.

Answer 4

not positive- but i believe (when accelerating quicker) the air intake sucks in more air, thus more fuel is added to keep the mixtures ratio the same.

also just a bit off topic-
the reason u use more fuel at say driving somewhere at 80 mph instead of 60 mph is the air resistance the car faces

Answer 5

I don't know...some cars (BMW for instance) has a gauge where the more you press on the gas, you can see how many gallons per mile you are using....

Answer 6

the faster you accelerate a given mass the more energy is required. therefore more is consumed to provide that force. force is mass times acceleration...